Willing is a much lower bar than able, which is what makes it usable on a bad day.
Nobody can feel warmth toward a difficult relative on command. What is available is noticing which story you are running about them, and holding it a little more loosely — the version where they are cruel, or the version where they are frightened and eighty and have been for years.
Neither reading is provable from where you stand. One of them costs considerably less to carry around all week.